What telomeres can tell us about the impact of urbanisation on birdlife

Differences in phenotypic traits such as morphology, physiology and behaviour, have been reported between urban and rural wildlife populations before. However, as the authors of a recent study published in Proceedings of the Royal Society B contend, how these differences affect the fitness of individuals is largely unknown.

The study which benefited from EU-funding for a Marie Curie Career Integration Grant for the project EUBITOX and a Marie Skłodowska-Curie grant for the project URBANEPIGENETICS, looked specifically at telomere shortening in great tits. Given telomere’s suspected links to senescence and mortality, their length was taken as an indicator of individual fitness amongst the urban and rural populations. The researchers studied the great tit, common to both environments, to investigate the link between telomere length (TL) and survival in both early and later life.

So what did the telomeres tell us?

Telomeres are strings of non-coding DNA at the ends of eukaryotic chromosomes and are known to contribute to maintaining genome stability. With each round of somatic cell division the telomeres shorten, and once they reach a critical length seem to influence the triggering of age-related decline.

The researchers in this study found that in both rural and urban habitats, TL was a strong predictor of post-fledging survival and subsequent recruitment into the population. However, crucially, they also found longer average TLs among the adult population in the urban environment, likely due to the selective disappearance of individuals with short telomeres early in life. They also found no difference between the urban and rural environments after recruitment, in terms of the link between TL and survival, possibly indicating that after its negative impact during early life, urban benefits may outweigh their costs as adult birds become better adapted.

Sweden’s third largest city Malmo, was selected or the urban study with the rural site located in a forest 37 km northeast of Malmo. For the urban study nest-boxes were distributed across four urban parks (10–45 ha) with a mix of coniferous and deciduous trees, grasslands, ponds and urban infrastructure, such as buildings and paved footpaths. Nest-boxes in the forest were distributed within a blend of forest patches (219 ha) dominated by Scots pine, oak and birch.

Blood sample were taken from nestlings at 15 days old, with parents caught and aged in the nest-boxes, when nestlings were 8 - 9 days old. Both nestlings and parents were also sexed, using DNA extracted from red blood cells in the case of nestlings and according to plumage characteristics for parents. In all, 217 urban and 327 rural samples were collected, between 2013 and 2015.

Understanding the impact of urbanisation

Around the world increasing urbanisation is having a major impact on the ecology and evolution of species, populations and communities. Urban areas contain a range of environmental factors not found in rural habitats, related to noise, night illumination, pollution levels, food resources, disease and predators. However, they present not only a range of challenges, but also opportunities in which some species, not only persist, but actually thrive. Food sources are available all year round and some bird species favour high-rise buildings as nesting sites.

Understanding the underlying mechanisms for variation in life-history traits will help teach us more about how species adapt to selection pressure. EUBITOX (European Urbanisation and its consequnces for Bird Health and Performance) was set up to focus specifically on nutrition and pollution factors between urban and rural populations, using a range of state-of-the-art methods in genetics, physiology and ecotoxicology. The URBANEPIGENETICS project was the first field and lab study to investigate how oxidative stress may play a significant role in epigenetic modifications in response to pollution, affecting development, disease resistance and ageing.

For more information:
CORDIS EUBITOX webpage
CORDIS URBANEPIGENETICS webpage